Remove an array element and shift the remaining ones

Question

How do I remove an element of an array and shift the remaining elements down  So  if I have an array    array    1 2 3 4 5     and want to delete 3 and shift the rest so I have   array    1 2 4 5    How would I go about this in the least amount of code

User · Answer

Programming Hub randomly provided a code snippet which in fact does reduce the length of an array  for  i   position to remove  i  lt  length of array    i            inputarray i    inputarray i   1       Not sure if it s behaviour that was added only later  It does the trick though

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Depending on your requirements  you may want to use stl lists for these types of operations  You can iterate through your list until you find the element  and erase the element  If you can t use lists  then you ll have to shift everything yourself  either by some sort of stl algorithm or manually

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std  copy does the job as far as moving elements is concerned     include  lt algorithm gt    std  copy array 3  array 5  array 2     Note that the precondition for copy is that the destination must not be in the source range  It s permissible for the ranges to overlap   Also  because of the way arrays work in C    this doesn t  shorten  the array  It just shifts elements around within it  There is no way to change the size of an array  but if you re using a separate integer to track its  size  meaning the size of the part you care about  then you can of course decrement that   So  the array you ll end up with will be as if it were initialized with   int array      1 2 4 5 5

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You can t achieve what you want with arrays   Use vectors instead  and read about the std  remove algorithm   Something like   std  remove array  array 5  3    will work on your array  but it will not shorten it  why -- because it s impossible   With vectors  it d be something like  v erase std  remove v begin    v end    3   v end

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You just need to overwrite what you re deleting with the next value in the array  propagate that change  and then keep in mind where the new end is   int array      1  2  3  4  5  6  7  8  9       delete 3  index 2  for  int i   2  i  lt  8    i      array i    array i   1      copy next element left   Now your array is  1  2  4  5  6  7  8  9  9   You cannot delete the extra 9 since this is a statically-sized array  you just have to ignore it  This can be done with std  copy   std  copy array   3     copy everything starting here           array   9     and ending here  not including it            array   2     to this destination   In C  11  use can use std  move  the algorithm overload  not the utility overload  instead   More generally  use std  remove to remove elements matching a value      remove  all  3 s  return new ending  remaining elements unspecified  auto arrayEnd   std  remove std  begin array   std  end array   3     Even more generally  there is std  remove if   Note that the use of std  vector lt int gt  may be more appropriate here  as its a  true  dynamically-allocated resizing array   In the sense that asking for its size   reflects removed elements

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If you are most concerned about code size and or performance  also for WCET analysis  if you need one   I think this is probably going to be one of the more transparent solutions  for finding and removing elements    unsigned int l 0  removed 0   for  unsigned int i 0  i lt count  i           if  array i     to remove           array l      array i       else         removed       count -  removed

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Just so it be noted  If the requirement to preserve the elements order is relaxed it is much more efficient to replace the element being removed with the last element

User · Answer

You can use memmove    but you have to keep track of the array size yourself   size t array size   5  int array 5     1  2  3  4  5       delete element at index 2 memmove array   2  array   3   array size - 2 - 1    sizeof int    array size--    In C    though  it would be better to use a std  vector   std  vector lt int gt  array     initialize array        delete element at index 2 array erase array begin     2

[c++] Remove an array element and shift the remaining ones

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